1. Field of the Invention
This invention pertains to catalyst material for expediting the oxidation of an olefin to the corresponding oxirane; and, more particularly to a catalyst material of a boron containing substance for catalyzing the liquid phase epoxidation of olefins with organic hydroperoxides.
2. Prior Art
Oxiranes or epoxides, while being valuable commercial products in and of themselves, are also commercially valuable as starting reactants for synthesizing many useful compounds such as polyether polyols for urethane systems. Over the years many methods have been disclosed for synthesizing such compounds. The majority of these methods involve the oxidation of the corresponding olefin. For example, it is known that ethylene can be converted to the corresponding epoxide by a vapor phase partial oxidation with molecular oxygen over a silver catalyst. However, the ease of olefin oxidation varies greatly depending upon the size and structure of the olefinic starting reactant and therefore many of the disclosed processes are not effective for epoxiding olefins in general.
Recently it has been disclosed that olefinically unsaturated organic compounds can be oxidized to the corresponding oxirane compound in liquid phase with organic hydroperoxides in the presence of various catalysts. For example, U.S. Pat. No. 3,350,422 issued Oct. 31, 1967 to Kollar discloses that soluble vanadium compounds can be employed as a homogeneous catalyst for oxidation of olefins with organic hydroperoxide. Specifically, hydrocarbon soluble organometallic compounds of vanadium are disclosed as being effective as epoxidation catalysts. However, the insoluble vanadium catalysts, such as for example, vanadium pentoxide are disclosed as substantially ineffective in catalyzing the epoxidation of propylene. More recently, U.S. Pat. No. 3,634,464 issued Jan. 11, 1972 to Wulff et al. describes the use of oxides of molybdenum on a solid inorganic oxide support modified by inclusion therewith of bismuth or certain rare earth metal oxides as a catalyst for the epoxidation of olefins with an organic hydroperoxide. The catalyst is substantially insoluble in the epoxidation reactant mixture, providing a heterogeneous system. The presence of a minor proportion of bismuth or certain rare earth oxides as catalyst modifiers is disclosed as a critical feature of the catalytic action.
Additionally, it has been disclosed that silicides or siliceous solids having high surface to mass ratio are particularly effective as catalytic substances in the epoxidation of olefins with organic hydroperoxides. Specifically, U.S. Pat. No. 3,702,855 issued Nov. 14, 1972 to Bell et al. discloses a catalytic material selected from metal silicides of titanium, zirconium, vanadium, mobium, chromium, molybdenum, and tungsten is effective as a liquid phase epoxidation catalysts.
More recently it has been disclosed in U.S. Pat. No. 3,832,363 issued Aug. 27, 1974 to Fetterly et al. that the epoxidation of ethylenic compounds to the corresponding oxirane compound is catalyzed by the presence of a boron oxide, a dehydrated boric acid, and the hydrocarbyl esters thereof. The compounds disclosed in this patent which are useful as catalysts contain at least one B--O--B linkage.
The previously described catalysts suffer from one or more disadvantages when employed as liquid phase epoxidation catalysts. For example, many of the previously known catalyst materials are expensive and difficult to prepare, and/or are highly selective to oxidation of specific olefinic compounds, and/or are difficult to use requiring special apparatus or highly selective reaction conditions, and/or are limited to heterogeneous or homogeneous type reaction systems.
Unexpectedly it has been found that a large class of boron containing substances are effective in catalyzing liquid phase epoxidation of an olefin with an organic hydroperoxide to the corresponding oxirane. These substances may be generally categorized as binary and ternary boride compounds consisting of boron and at least one element selected from groups II-A, III-B, IV-B, V-B, VI-B, VII-B, VIII, III-A, IV-A and V-A of the Periodic Table, the rare earths and the actinides. Because of the wide range of boron containing substances effective in catalyzing liquid phase epoxidation of an olefin with an organic hydroperoxide, the catalyst may be selected to form a substantially heterogeneous system with the reactants or a substantially homogeneous system with the reactants. Further, boron containing substances of the instant invention are easily obtainable, relatively inexpensive and easy to handle. Because of the wide range of boron substances which are shown catalytically active, a particular compound can be matched to a particular epoxidation reaction thus achieving somewhat superior selectivity and yield. Mixtures of these boron substances can also be used to afford specific selectivity.